ANOMALIES IN CELL-VOLUME AND ELECTRONIC-PROPERTIES IN GETTER ANNEALEDYBA2(CUM)(3)O-Y, M=NI

Structural and magnetic data on getter annealed YBa2(Cu0.95M0.05)(3)O- y, M=Ni are presented. Similar to unsubstituted materials, but differe nt from M=Fe, getter annealings at intermediary temperatures (753 K) p roduce an extended orthorhombic superconducting region with abrupt cel l volume (V) shrinkage around y similar to 6.50. This orthorhombicity, denoted O42, corresponds most nearly to conventional phenomenology wi th long chains on Cu(1) with four-(1)4- and two fold-(1)2- O coordinat ion. 673 K annealings produce a smaller orthorhombic range with consid erable reduction in T-c. This region is diagnosed to be based on new s tructural motifs with larger amounts of orthorhombically arranged thre e fold O coordination (1)3. A yet stronger trend to orthorhombicity ba sed on (1)3, denoted O3, pertains to high temperature annealings (1023 K) which produce a monotonic structural development in c-axis with no stepwise contraction and absence of T-c to y similar to 6.8. This is also the behavior obtained on direct quenching from elevated temperatu res which can in addition result in anomalous cell volume expansion ef fects (V+) near y=6.5. These materials are further distinguished in th at they do not superconduct when reoxygenated up to y similar to 6.8. A general distinction in the phenomenology of RBa2Cu3Oy is accordingly made between O filling based on (1)3 e.g. (1)3(1)4 (K phenomenology) and (1)2(1)4 (D, or disproportionation phenomenology). In connection w ith extrapolations from low temperature T-c annealing effects it is re alized that O42 pertains only to a limited low temperature modificatio n with reversible ladder type transitions to O3 at intermediary temper atures for substituted and unsubstituted compounds. (C) 1998 Elsevier Science S.A.